Formation of Oxalate from the Mg(OH)₂‐Based Peroxide Bleaching of Mechanical Pulps

Abstract

Oxalate is a major source of scaling during the manufacturing process of bleached mechanical pulps and the majority is formed during the peroxide bleaching stage. In this paper, we investigated the effect of using Mg(OH) 2 as an alkali source during peroxide bleaching on the formation of oxalate and its partition between soluble and precipitated oxalates. We found that at the same brightness target, the total amount of oxalate formed is similar between the Mg(OH) 2 -based peroxide system and the conventional NaOH-based system, however, almost all of the newly formed oxalate from the former was found in the soluble state, while in the NaOH-based peroxide process, a large fraction is in the precipitate form. Therefore, the oxalate-related scaling is significantly less or even negligible during the Mg(OH) 2 -based peroxide process. The underlying mechanism accounting for the above observation will be discussed.

A Review of Recent Technological Advances in the Brightening of High‐Yield Pulps

“…The pulp fibres of the TMP are well developed, and the change in alkalinity from the NaOHbased process to the Mg(OH) 2 -based process would have a negligible effect on fibre development for the TMP. Other benefits of the Mg(OH) 2 -based peroxide process include: • decreased bleaching cost (Li et al, In press); • decreased anionic trash formation (Li et al, In press; He et al, submitted); • Elimination of oxalate-related scaling (Yu et al, 2004).…”

The influence of temperature and moisture on the physical properties of cellulose in the presence of metal chlorides and glucuronic acid

“…Magnesium salts are sometimes added to the pulp; magnesium sulfate is added to stabilizing hydrogen peroxide during bleaching, magnesium hydroxide is used instead of sodium hydroxide, and magnesium salts can be added to avoid scaling, (Colodette et al 1989;He et al 2004;Yu et al 2004). It is therefore important to increase our knowledge how alkaline earth metals influences the viscosity of the pulp.…”

The influence of temperature and moisture on the optical properties of cellulose in the presence of metal chlorides and glucuronic acid

“…Magnesium sulfate is added for stabilizing hydrogen peroxide during bleaching, magnesium hydroxide is used instead of sodium hydroxide, and magnesium salts can also be added to avoid scaling (Colodette et al 1989;He et al 2004;Yu et al 2004). It is therefore important to increase our knowledge how alkaline earth metals influences the color stability of the pulp.…”